Oxygen steam combustion technology is concerned greatly with the characteristics of high efficiency and near-zero emissions. The combustion characteristics of syngas under oxygen steam conditions were studied experimentally in this paper. The gas composition and flame temperature in the center of the combustor chamber were measured under the H2O/O2 of 2.0 on a diffusion combustion experimental setup. The effects of excess amount of oxygen on the combustion process of syngas under the oxygen steam conditions were discussed. The results showed that most of the H2 and CO combusted within the first 28 ms when the excess amount of oxygen was zero. The burn rate of H2 was greater with higher burnout

but the burn rate of CO was lower and the content in the exit of combustor was still high. When the excess coefficient of oxygen was increased from 0 to 10%

the overall concentration of CO reduced with increasing burning rate and the combustion flame temperature increased in the earlier stage. The concentration of CO in the combustor exit decreased gradually with increasing excess coefficient of oxygen. The concentration of CO in the combustor exit decreased rapidly with the small excess oxygen

while continuing to increase the amount of excess oxygen

the concentration of CO decreased slowly.